1. Technical Field
The present invention relates to a light guide, an illuminating device for image reading, and an image reading apparatus, and more particularly to an image reading apparatus configured to optically read an image of a document, and a light guide and an illuminating device for use in the image reading apparatus.
2. Description of Related Art
In an image reading apparatus called a scanner, generally, either a reading system including an illumination unit extending in a main-scanning direction or an object, such as a document, to be subjected to image reading is moved in a sub-scanning direction, so that the image of the document can be read two-dimensionally. As a light source for the image reading, a fluorescent lamp is conventionally used. In recent years, however, replacement of the fluorescent lamp with an LED is accelerated. Unlike a fluorescent lamp, an LED is a point light source. Therefore, when an LED is used as a light source in an image reading apparatus, normally, a light guide as disclosed by Japanese Patent Laid-Open Publication No. 2013-51108 is also used so as to achieve linear light distribution needed for scanning. Such a light guide 510 (see FIG. 12) reflects light input from the LED on a reflecting surface provided therein and outputs the reflected light toward a predetermined image reading point through an emitting surface. With such a conventional light guide, however, all of the light rays reflected by the reflecting surface are not directed to the predetermined image reading point A, and some of the reflected light rays travel to places far away from the image reading point A as illustrated in FIG. 12. Thus, such a conventional light guide has a low irradiation efficiency.